/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize.evaluation;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;
import proguard.evaluation.BasicInvocationUnit;
import proguard.evaluation.value.*;
import proguard.util.ArrayUtil;

/**
 * This AttributeVisitor analyzes the liveness of the variables in the code attributes that it visits, based on partial
 * evaluation.
 *
 * @author Eric Lafortune
 */
public class LivenessAnalyzer extends SimplifiedVisitor
    implements AttributeVisitor, InstructionVisitor, ExceptionInfoVisitor {
    // *
    private static final boolean DEBUG = false;
    /*/
    private static       boolean DEBUG = System.getProperty("la") != null;
    //*/

    private static final int MAX_VARIABLES_SIZE = 64;

    private final PartialEvaluator partialEvaluator;
    private final boolean runPartialEvaluator;
    private final InitializationFinder initializationFinder;
    private final boolean runInitializationFinder;

    private long[] isAliveBefore = new long[ClassConstants.TYPICAL_CODE_LENGTH];
    private long[] isAliveAfter = new long[ClassConstants.TYPICAL_CODE_LENGTH];
    private long[] isCategory2 = new long[ClassConstants.TYPICAL_CODE_LENGTH];

    // Fields acting as global temporary variables.
    private boolean checkAgain;
    private long alive;

    /**
     * Creates a new LivenessAnalyzer.
     */
    public LivenessAnalyzer() {
        this(new ReferenceTracingValueFactory(new BasicValueFactory()));
    }

    /**
     * Creates a new LivenessAnalyzer. This private constructor gets around the constraint that it's not allowed to add
     * statements before calling 'this'.
     */
    private LivenessAnalyzer(ReferenceTracingValueFactory referenceTracingValueFactory) {
        this(new PartialEvaluator(referenceTracingValueFactory,
            new ReferenceTracingInvocationUnit(new BasicInvocationUnit(referenceTracingValueFactory)), true,
            referenceTracingValueFactory), true);
    }

    /**
     * Creates a new LivenessAnalyzer. This private constructor gets around the constraint that it's not allowed to add
     * statements before calling 'this'.
     */
    private LivenessAnalyzer(PartialEvaluator partialEvaluator, boolean runPartialEvaluator) {
        this(partialEvaluator, runPartialEvaluator, new InitializationFinder(partialEvaluator, false), true);
    }

    /**
     * Creates a new LivenessAnalyzer that will use the given partial evaluator and initialization finder.
     * 
     * @param partialEvaluator the evaluator to be used for the analysis.
     * @param runPartialEvaluator specifies whether to run this evaluator on every code attribute that is visited.
     * @param initializationFinder the initialization finder to be used for the analysis.
     * @param runInitializationFinder specifies whether to run this initialization finder on every code attribute that
     *        is visited.
     */
    public LivenessAnalyzer(PartialEvaluator partialEvaluator, boolean runPartialEvaluator,
        InitializationFinder initializationFinder, boolean runInitializationFinder) {
        this.partialEvaluator = partialEvaluator;
        this.runPartialEvaluator = runPartialEvaluator;
        this.initializationFinder = initializationFinder;
        this.runInitializationFinder = runInitializationFinder;
    }

    /**
     * Returns whether the instruction at the given offset has ever been executed during the partial evaluation.
     */
    public boolean isTraced(int instructionOffset) {
        return partialEvaluator.isTraced(instructionOffset);
    }

    /**
     * Returns whether the specified variable is alive before the instruction at the given offset.
     */
    public boolean isAliveBefore(int instructionOffset, int variableIndex) {
        return variableIndex >= MAX_VARIABLES_SIZE
            ? partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex) != null
            : (isAliveBefore[instructionOffset] & (1L << variableIndex)) != 0;
    }

    /**
     * Sets whether the specified variable is alive before the instruction at the given offset.
     */
    public void setAliveBefore(int instructionOffset, int variableIndex, boolean alive) {
        if (variableIndex < MAX_VARIABLES_SIZE) {
            if (alive) {
                isAliveBefore[instructionOffset] |= 1L << variableIndex;
            } else {
                isAliveBefore[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }

    /**
     * Returns whether the specified variable is alive after the instruction at the given offset.
     */
    public boolean isAliveAfter(int instructionOffset, int variableIndex) {
        return variableIndex >= MAX_VARIABLES_SIZE
            ? partialEvaluator.getVariablesAfter(instructionOffset).getValue(variableIndex) != null
            : (isAliveAfter[instructionOffset] & (1L << variableIndex)) != 0;
    }

    /**
     * Sets whether the specified variable is alive after the instruction at the given offset.
     */
    public void setAliveAfter(int instructionOffset, int variableIndex, boolean alive) {
        if (variableIndex < MAX_VARIABLES_SIZE) {
            if (alive) {
                isAliveAfter[instructionOffset] |= 1L << variableIndex;
            } else {
                isAliveAfter[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }

    /**
     * Returns whether the specified variable takes up two entries after the instruction at the given offset.
     */
    public boolean isCategory2(int instructionOffset, int variableIndex) {
        return variableIndex >= MAX_VARIABLES_SIZE
            ? partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex) != null
                && partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex).isCategory2()
            : (isCategory2[instructionOffset] & (1L << variableIndex)) != 0;
    }

    /**
     * Sets whether the specified variable takes up two entries after the instruction at the given offset.
     */
    public void setCategory2(int instructionOffset, int variableIndex, boolean category2) {
        if (variableIndex < MAX_VARIABLES_SIZE) {
            if (category2) {
                isCategory2[instructionOffset] |= 1L << variableIndex;
            } else {
                isCategory2[instructionOffset] &= ~(1L << variableIndex);
            }
        }
    }

    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        // DEBUG =
        // clazz.getName().equals("abc/Def") &&
        // method.getName(clazz).equals("abc");

        if (DEBUG) {
            System.out.println();
            System.out.println(
                "Liveness analysis: " + clazz.getName() + "." + method.getName(clazz) + method.getDescriptor(clazz));
        }

        int codeLength = codeAttribute.u4codeLength;
        int variablesSize = codeAttribute.u2maxLocals;

        // Initialize the global arrays.
        isAliveBefore = ArrayUtil.ensureArraySize(isAliveBefore, codeLength, 0L);
        isAliveAfter = ArrayUtil.ensureArraySize(isAliveAfter, codeLength, 0L);
        isCategory2 = ArrayUtil.ensureArraySize(isCategory2, codeLength, 0L);

        // Evaluate the method.
        if (runPartialEvaluator) {
            partialEvaluator.visitCodeAttribute(clazz, method, codeAttribute);
        }

        if (runInitializationFinder) {
            initializationFinder.visitCodeAttribute(clazz, method, codeAttribute);
        }

        // We'll only really analyze the first 64 variables.
        if (variablesSize > MAX_VARIABLES_SIZE) {
            variablesSize = MAX_VARIABLES_SIZE;
        }

        // Mark liveness blocks, as many times as necessary.
        do {
            checkAgain = false;
            alive = 0L;

            // Loop over all traced instructions, backward.
            for (int offset = codeLength - 1; offset >= 0; offset--) {
                if (partialEvaluator.isTraced(offset)) {
                    // Update the liveness based on the branch targets.
                    InstructionOffsetValue branchTargets = partialEvaluator.branchTargets(offset);
                    if (branchTargets != null) {
                        // Update the liveness right after the branch instruction.
                        alive = combinedLiveness(branchTargets);
                    }

                    // Merge the current liveness.
                    alive |= isAliveAfter[offset];

                    // Update the liveness after the instruction.
                    isAliveAfter[offset] = alive;

                    // Update the current liveness based on the instruction.
                    codeAttribute.instructionAccept(clazz, method, offset, this);

                    // Merge the current liveness.
                    alive |= isAliveBefore[offset];

                    // Update the liveness before the instruction.
                    if ((~isAliveBefore[offset] & alive) != 0L) {
                        isAliveBefore[offset] = alive;

                        // Do we have to check again after this loop?
                        InstructionOffsetValue branchOrigins = partialEvaluator.branchOrigins(offset);
                        if (branchOrigins != null && offset < branchOrigins.maximumValue()) {
                            checkAgain = true;
                        }
                    }
                }
            }

            // Account for the liveness at the start of the exception handlers.
            codeAttribute.exceptionsAccept(clazz, method, this);
        } while (checkAgain);

        // Loop over all instructions, to mark variables that take up two entries.
        for (int offset = 0; offset < codeLength; offset++) {
            if (partialEvaluator.isTraced(offset)) {
                // Loop over all variables.
                for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++) {
                    // Is the variable alive and a category 2 type?
                    if (isAliveBefore(offset, variableIndex)) {
                        Value value = partialEvaluator.getVariablesBefore(offset).getValue(variableIndex);
                        if (value != null && value.isCategory2()) {
                            // Mark it as such.
                            setCategory2(offset, variableIndex, true);

                            // Mark the next variable as well.
                            setAliveBefore(offset, variableIndex + 1, true);
                            setCategory2(offset, variableIndex + 1, true);
                        }
                    }

                    // Is the variable alive and a category 2 type?
                    if (isAliveAfter(offset, variableIndex)) {
                        Value value = partialEvaluator.getVariablesAfter(offset).getValue(variableIndex);
                        if (value != null && value.isCategory2()) {
                            // Mark it as such.
                            setCategory2(offset, variableIndex, true);

                            // Mark the next variable as well.
                            setAliveAfter(offset, variableIndex + 1, true);
                            setCategory2(offset, variableIndex + 1, true);
                        }
                    }
                }
            }
        }

        if (DEBUG) {
            // Loop over all instructions.
            for (int offset = 0; offset < codeLength; offset++) {
                if (partialEvaluator.isTraced(offset)) {
                    long aliveBefore = isAliveBefore[offset];
                    long aliveAfter = isAliveAfter[offset];
                    long category2 = isCategory2[offset];

                    // Print out the liveness of all variables before the instruction.
                    for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++) {
                        long variableMask = (1L << variableIndex);
                        System.out.print(
                            (aliveBefore & variableMask) == 0L ? '.' : (category2 & variableMask) == 0L ? 'x' : '*');
                    }

                    // Print out the instruction itself.
                    System.out.println(" " + InstructionFactory.create(codeAttribute.code, offset).toString(offset));

                    // Print out the liveness of all variables after the instruction.
                    for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++) {
                        long variableMask = (1L << variableIndex);
                        System.out.print(
                            (aliveAfter & variableMask) == 0L ? '.' : (category2 & variableMask) == 0L ? 'x' : '=');
                    }

                    System.out.println();
                }
            }
        }
    }

    // Implementations for InstructionVisitor.

    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset,
        Instruction instruction) {}

    public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset,
        VariableInstruction variableInstruction) {
        int variableIndex = variableInstruction.variableIndex;
        if (variableIndex < MAX_VARIABLES_SIZE) {
            long livenessMask = 1L << variableIndex;

            // Is it a load instruction or a store instruction?
            if (variableInstruction.isLoad()) {
                // Start marking the variable before the load instruction.
                alive |= livenessMask;
            } else {
                // Stop marking the variable before the store instruction.
                alive &= ~livenessMask;

                // But do mark the variable right after the store instruction.
                isAliveAfter[offset] |= livenessMask;
            }
        }
    }

    public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset,
        ConstantInstruction constantInstruction) {
        // Special case: variable 0 ('this') in an initializer has to be alive
        // as long as it hasn't been initialized.
        if (offset == initializationFinder.superInitializationOffset()) {
            alive |= 1L;
        }
    }

    // Implementations for ExceptionInfoVisitor.

    public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute,
        ExceptionInfo exceptionInfo) {
        // Are any variables alive at the start of the handler?
        long alive = isAliveBefore[exceptionInfo.u2handlerPC];
        if (alive != 0L) {
            // Set the same liveness flags for the entire try block.
            int startOffset = exceptionInfo.u2startPC;
            int endOffset = exceptionInfo.u2endPC;

            for (int offset = startOffset; offset < endOffset; offset++) {
                if (partialEvaluator.isTraced(offset)) {
                    if ((~(isAliveBefore[offset] & isAliveAfter[offset]) & alive) != 0L) {
                        isAliveBefore[offset] |= alive;
                        isAliveAfter[offset] |= alive;

                        // Check again after having marked this try block.
                        checkAgain = true;
                    }
                }
            }
        }
    }

    // Small utility methods.

    /**
     * Returns the combined liveness mask of the variables right before the specified instruction offsets.
     */
    private long combinedLiveness(InstructionOffsetValue instructionOffsetValue) {
        long alive = 0L;

        int count = instructionOffsetValue.instructionOffsetCount();
        for (int index = 0; index < count; index++) {
            alive |= isAliveBefore[instructionOffsetValue.instructionOffset(index)];
        }

        return alive;
    }
}
